Printed circuits are populated with integrated circuits, transducers, and other components. Printed circuits are mounted in the interior of electronic device housings. For example, printed circuits may be mounted in the interior of a cellular telephone or computer housing or other electronic device housing.
Some printed circuits are installed within the interiors of waterproof housings. In sealed environments such as these, the risk of exposing sensitive components to moisture is minimal. In many situations, however, printed circuits are installed within housings that provide a degree of environmental protection, but that are not completely waterproof. When installed in this type of device housing, there is a risk that sensitive components on a printed circuit may be exposed to moisture during normal device operation.
To reduce the sensitivity of components on a printed circuit to exposure to moisture, the components can he protected with a conformal coating. The conformal coating may cover the surface of a printed circuit and may prevent moisture damage by repelling liquids.
Conformal coatings may be deposited as blanket films. Effective sealing can be achieved by using conformal coating materials that cover all exposed surfaces of the components on a printed circuit board, even in scenarios in which the components have uneven heights and a variety of different shapes. The ability of conformal coating to coat complex surfaces without forming gaps allows the conformal coating to form a satisfactory environmental barrier, but can make it difficult to mask off portions of the printed circuit board. It can therefore be difficult to form openings in the conformal coating for test points, electrical connectors, and other components.